Optimisation of tube voltage for conventional urography using a Gd2O2S:Tb flat panel detector

• Published in: Radiation protection dosimetry 2010-04, Vol.139 (1-3), p.86-91
• Main Authors: Zachrisson, Sara, Hansson, Jonny, Cederblad, Åke, Geterud, Kjell, Båth, Magnus
• Format: Article
• Language: English
• Subjects: Algorithms; Equipment Design; Equipment Failure Analysis; Information Storage and Retrieval - methods; Radiographic Image Enhancement - instrumentation; Radiographic Image Enhancement - methods; Radiographic Image Interpretation, Computer-Assisted - instrumentation; Radiographic Image Interpretation, Computer-Assisted - methods; Radiologi och bildbehandling; Radiology, Nuclear Medicine and Medical Imaging; Reproducibility of Results; Sensitivity and Specificity; Urography - instrumentation; Urography - methods; X-Ray Intensifying Screens
• ISSN: 0144-8420; 1742-3406; 1742-3406
• DOI: 10.1093/rpd/ncq101

With the increasing use of computed tomography (CT) for urography examinations, the indications for ‘conventional’ projection urography have changed and are more focused on high-contrast details. The purpose of the present study was to optimise the beam quality for urography examinations performed with a Gd2O2S:Tb flat-panel detector for the new conditions. Images of an anthropomorphic phantom were collected at different tube voltages with a CXDI-40G detector (Canon Inc., Tokyo, Japan). The images were analysed by radiologists and residents in a visual grading characteristics (VGCs) study. The tube voltage resulting in the best image quality was 55 kV, which therefore was selected for a clinical study. Images from 62 patients exposed with either 55 or 73 kV (original tube voltage) at constant effective doses were included. The 55-kV images underwent simulated dose reduction to represent images collected at 80, 64, 50, 40 and 32 % of the original dose level. All images were included in a VGC study where the observers rated the visibility of important anatomical landmarks. For images collected at 55 kV, an effective dose of ∼85 % resulted in the same image quality as for images collected at 73 kV at 100 % dose. In conclusion, a low tube voltage should be used for conventional urography focused on high-contrast details. The study indicates that using a tube voltage of 55 kV instead of 73 kV for a Gd2O2S:Tb flat-panel detector, the effective dose can be reduced by ∼10–20 % for normal-sized patients while maintaining image quality.